123One of the purposes of the present invention is to provide a probe for imaging a protein having a sheet structure for the purpose of diagnosing conformation diseases particularly diseases in which the accumulation of tau protein in the brain is observed as the main characteristic symptom (tauopathy) such a Alzheimer s disease. Another one of the purposes of the present invention is to provide a compound which has high specificity to tau enables the imaging of tau with good sensitivity has high brain migration properties is accumulated in bones in a minute amount or is not accumulated in bones and has low toxicity or does not have toxicity. The present invention achieves the above mentioned purposes by providing a compound represented by formula (I) (wherein A R R R and others are as defined in the description) or a pharmaceutically acceptable salt or solvate thereof.
